Small electric motor with axial bearing

ABSTRACT

A small electric motor has a rotor with a permanent magnet and a shaft having a first end provided with a depression. Axial and radial bearings support the shaft. A bushing receives the first end of the shaft. The axial bearing has a non-magnetic ball positioned in the depression. A side of the ball remote from the shaft runs against a running surface of the bushing. The shaft is magnetically loaded toward the running surface so that the ball is forced against the running surface. The shaft is ferromagnetic and part of a magnetic circuit of the permanent magnet. The ball forms an air gap at the first shaft end. An end face of the shaft facing the air gap forms a magnetic pole that attracts magnetic particles in the area of the axial bearing and keeps them away from the running surface to counteract destruction of running surface and ball.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a small electric motor.

2. Description of Related Art

Known small motors are constructed such that the shafts of the rotorsare comprised of steel and have a substantially semi-spherical cap atthe shaft end which runs against a contact surface. A disadvantage ofsuch bearings is that the cap of the shaft end acts like a magnetic poleand attracts magnetic particles and, in this way, can damage the bearinglocation prematurely and finally destroy it. The magnetic pole resultsfrom the shaft being comprised of ferromagnetic material and the rotorcontaining a permanent magnet whose magnetic field closes across theshaft.

Such damaged bearing locations cause strong noises which are notpermissible, in particular, in the case of small electric motorsrunning, for example, in air-conditioning devices of motor vehicles.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a bearing which does nothave the aforementioned disadvantages.

The solution to this object resides in that the axial bearing comprisesa non-magnetic ball which is arranged in a depression centrally providedwithin one end of the shaft and is guided by the rim of this depressionand runs with its side facing away from the shaft against the runningsurface of a bushing, or in that a depression with a rim is provided atone end of the shaft and a non-magnetic ball is fastened in thedepression, wherein the part of the ball projecting from the shaft endruns against a running surface of a bushing. Further details andadvantageous developments of the invention result from the embodimentsdescribed in the following and illustrated in the drawing.

Further details and advantageous developments of the invention resultfrom the embodiments described in the following and illustrated in thedrawing as well as from the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

It is shown in:

FIG. 1 an axial section of one embodiment of a bearing according to theinvention in a small ventilator;

FIG. 2 an enlarged illustration of detail II of the embodiment accordingto FIG. 1; and

FIG. 3 a further embodiment of a bearing according to the invention asan enlarged detail view.

DESCRIPTION OF PREFERRED EMBODIMENTS

As an exemplary application a small ventilator 10, as they are used, forexample, as a sensor ventilator in air-conditioning devices of motorvehicles, is illustrated in FIG. 1 and is driven by a small motoraccording to the invention.

This known ventilator 10 is described only to such an extent as isrequired for this invention. The drive motor of the ventilator 10,preferably an electrically commutated direct current motor, comprises arotor with a permanent magnet 15 and a ventilator wheel 12 fastened onthe rotor and comprising a hub 13 having a shaft 1 fastened in itscenter.

The shaft 1 is radially supported in a bearing 11 which is mounted in abearing support tube 14. A ball 3 is placed into a depression 2 providedin one end of the shaft 1. This ball is comprised of a non-magnetic andwear-resistant material such as, for example, stone, ceramic material,plastic material, or metal. Such balls having a high surface quality anda very smooth surface can be procured very inexpensively asmass-produced articles, for example, from the watch and clock makingindustry, i.e., such a bearing require only minimal extra costs andeffects a noise level with respect to the axial bearing action which isno longer audible in connection with such small ventilators.

FIG. 2 shows an enlarged detail of the shaft 1 of steel with the ball 3which is inserted into the depression 2 of the shaft 1. For facilitatingmounting of the ball 3, the depression 2 has an angle of approximately90° and a depth T of approximately 0.3 of the diameter of the ball. Theshaft 1 of the rotor is loaded, as is known in the art, by means of adefined magnetic force in the axial direction and forces in this way theball 3 against the running surface 5 of a bushing 4 and simultaneouslyprovides an axial securing action of the rotor against falling out, forexample, during transport. In this connection, a magnetic pole is formedat one rim 6 which attracts magnetic particles 7, which result frommounting or wear, and these particles 7 are thus kept away from theaxial bearing location between the ball 3 and the running surface 5.These particles 7 are generally hard-magnetic particles (for example,from the permanent magnet of the rotor) which cause great wear and thusresult in a fast destruction of the bearing locations.

FIG. 3 shows a further embodiment of the inventive bearing. Thedepression 2 at the end of the shaft 1 is configured in this embodimentsuch that the ball 3 projects approximately halfway into the end of theshaft. The rim 6 of the depression 2 can secure the ball 3 by means ofcaulking. The ball 3 can also be connected by means of an adhesive withthe end of the shaft.

The invention is not limited to the illustrated and describedembodiments but also comprises all embodiments which act in the same waywithin the meaning of the invention.

What is claimed is:
 1. A small electric motor comprising: a rotorcomprising a permanent magnet (15) and a shaft (1) having a first endprovided with a depression (2); an axial bearing (3, 5) and a radialbearing (11) supporting the shaft (1) axially and radially,respectively; a bushing (4) receiving the first end of the shaft (1) andhaving a running surface (5); wherein the axial bearing (3, 5) comprisesa non-magnetic ball (3), wherein the ball (3) is positioned in thedepression (2) of the shaft (1) and has a side facing away from theshaft (1) and running against the running surface (5) of the bushing(4); wherein the shaft (1) is magnetically loaded in a direction towardthe running surface (5) of the bushing (4) so that the ball (3) isforced against the running surface (5) of the bushing (4); wherein theshaft (1) is comprised of a ferromagnetic material and forms a part of amagnetic circuit of the permanent magnet (15) of the rotor; wherein theball (3) forms an air gap at the first end of the shaft (1); and whereinan end face of the shaft (1) facing the air gap forms a magnetic pole(6), wherein the magnetic pole (6) attracts magnetic particles (7) inthe area of the axial bearing (3, 5) and keeps the magnetic particles(7) away from the running surface (5) to counteract a destruction of therunning surface (5) and of the non-magnetic ball (3) by the magneticparticles (7).
 2. A small motor according to claim 1, wherein the ball(3) is comprised of stone material.
 3. A small motor according to claim1, wherein the ball (3) is comprised of ceramic material.
 4. A smallmotor according to claim 1, wherein the ball (3) is comprised of plasticmaterial.
 5. A small motor according to claim 1, wherein the ball (3)has a smooth surface.
 6. A small ventilator comprising a small electricmotor according to claim 1.